1. Field of the Invention
The present invention relates to a fuel cell system and a vehicle equipped with a fuel cell.
2. Description of Related Art
In Japanese Patent Application Publication No. 2013-145709, a technique is described in which, when an operation of a fuel cell is stopped, an increase and a decrease in current output from the fuel cell are periodically repeated so as not to allow an oxidizing gas to remain in an internal section (cathode) of the fuel cell after the operation is stopped, such that the oxidizing gas is efficiently consumed. When the oxidizing gas is consumed, a flow dividing valve is fully turned to a bypass side, and a pressure regulating valve is fully opened.
Oxygen that is not consumed moves to an anode through an electrolyte film after the operation of the fuel cell is ended. On the other hand, since the anode contains impurities such as nitrogen moved from a cathode, there may be case where the partial pressure of hydrogen in the anode is low. In the case where the partial pressure of hydrogen is low, hydrogen and oxygen may react with each other in the anode and an electromotive force is generated in a surface of the anode electrode. In addition, the durability of a catalyst may be degraded. When hydrogen is supplied to the anode in order to increase the partial pressure of hydrogen, the amount of hydrogen penetrating the cathode is increased. Therefore, when the hydrogen in the cathode is discharged during a subsequent start-up, the concentration of hydrogen in emissions is increased. In addition, the total pressure of the anode is increased, and this is disadvantageous in terms of an injection pressure at which hydrogen is injected into the anode, or the pressure resistance of the anode.